The Careless Whisper singer was found dead at his home in Oxfordshire, England, on Christmas Day (25Dec16). His publicist revealed at the time that his passing was caused by heart failure, but results from an initial post-mortem examination were inconclusive.

Toxicology tests are now being conducted on Michael's body and Britain's The Sun newspaper reports police are concerned the singer's death may have been caused by an overdose of drugs.

According to the newspaper, detectives from Thames Valley Police Major Crime Unit have been called in to look into the singer's death in more detail.

"The investigation is now picking up a bit of speed," a source told the publication. "Officers from the Major Crime Unit have begun asking questions of those who were in the area at the time George died and the days before.

"They want to build up an idea of what George’s last seven days were like and who came and went. These individuals now handling the day-to-day inquiries have worked on some very serious crimes so are well placed to assist with this."

To aid their investigation, detectives have asked a leading photographic agency in London to hand over all pictures of the singer's house in the lead-up to his death. They are also apparently set to question Michael's on-off boyfriend Fawaz, who has delivered conflicting accounts of what happened on the day of the singer's passing.

The hairdresser originally alleged he had spent the weekend at George's house, saying: "Everything had been very complicated recently, but George was looking forward to Christmas and so was I.”

But Fawaz then said he had slept in his car on Christmas Eve, before finding the 53-year-old singer dead on Christmas Day.

Fawaz also hit headlines when a series of posts appeared on his Twitter page, in which he appeared to allege that Michael had taken his own life.

He later said his account had been hacked, and shut down his profile in the wake of the incident.